fixed-typed-arena

An arena that allocates values of a single type (similar to typed-arena) using chunks of memory that have a configurable fixed size. This enables it to perform allocations in non-amortized O(1) (constant) time.

Other arena implementations, like typed-arena, are optimized for throughput: they allocate chunks of memory with exponentially increasing sizes, which results in amortized constant-time allocations.

fixed-typed-arena is optimized for latency: it allocates chunks of memory with a fixed, configurable size, and individual value allocations are performed in non-amortized constant time.

This crate depends only on core and alloc, so it can be used in no_std environments that support alloc.

Example

use fixed_typed_arena::Arena;
struct Item(u64);

let arena = Arena::<_, 128>::new();
let item1 = arena.alloc(Item(1));
let item2 = arena.alloc(Item(2));
item1.0 += item2.0;

assert_eq!(item1.0, 3);
assert_eq!(item2.0, 2);

References

Items allocated by an Arena can contain references with the same life as the arena itself, including references to other items, but the crate feature dropck_eyepatch must be enabled. This requires Rust nightly, as fixed-typed-arena must use the eponymous unstable language feature.

Alternatively, you may be able to use a ManuallyDropArena instead.

ManuallyDropArena

This crate also provides ManuallyDropArena, which is like Arena but returns references of any lifetime, including 'static. The advantage of this type is that it can be used without being borrowed, but it comes with the tradeoff that it will leak memory unless the unsafe drop method is called.

Iteration

fixed-typed-arena’s arena types allow iteration over all allocated items. Safe mutable iteration is provided for Arena, and safe immutable iteration is provided for all arena types if Options::Mutable is false. Unsafe mutable and immutable iteration is provided for all arena types regardless of options.